H2S is present in a number of industrial gas streams that include landfill gas, digester gas, natural gas, coal gas and sewer gas, for example. H2S can be removed from gas streams by contacting said gas streams with solid adsorbents comprising oxides, hydroxides, carbonates, or mixtures thereof of magnesium, chromium, manganese, iron, cobalt, zinc and/or copper wherein said metals present as oxides, hydroxides, carbonate, or mixtures thereof, are able to form sulfides upon contact with H2S. Iron, zinc and copper are the preferred metals. As an example, hydroxides of iron, zinc and copper will react with H2S to yield the corresponding metal sulfide. These reactions proceed as follows:2FeOOH+3H2S→Fe2S3+4H2O  (1)Zn(OH)2+H2S→ZnS+2H2O  (2)Cu(OH)2+H2S→CuS+2H2O  (3)The above reactions are known to one skilled in the art. In treating process gas containing H2S, it is desirable that oxygen and water be present in order to improve the H2S removal capacity of the media via regeneration of the active sites. Otherwise, the H2S removal capacity of the media will be limited to the number of available reaction sites. Regeneration reactions involving water and oxygen are postulated to proceed as follows:Fe2S3+3H2O→Fe2(SH)3(OH)3 Fe2(SH)3(OH)3+9/2O2→Fe2O3+3SO2+3H2Oor 2FeOOH+3SO2+2H2Oor Fe2(SO3)3+3H2O  (4)ZnS+H2O→Zn(SH)(OH)Zn(SH)(OH)+3/2O2→ZnO+SO2+H2Oor Zn(OH)2+SO2 or ZnSO3+H2O  (5)CuS+H2O→Cu(SH)(OH)Cu(SH)(OH)+3/2O2→CuO+SO2+H2Oor Cu(OH)2+SO2 or CuSO3+H2O  (6)From the above reaction sequences, the metal sulfide is first hydrated with water, then oxidized to yield the metal oxide plus sulfur dioxide, the metal hydroxide plus sulfur dioxide, and/or metal sulfite. Sulfur dioxide will then react with H2S to yield elemental sulfur plus water, whereas the metal sulfite will react with H2S to yield elemental sulfur and the corresponding metal oxide and/or hydroxide:SO2+2H2S→3S+2H2O  (7)orMSO3+2H2S→MO+3S+2H2Oor M(OH)2+3S  (8)wherein MSO3 represents a metal sulfite. From the above reaction schemes, note that the O2/H2S ratio is 1.5. Thus, it becomes necessary that the concentration of oxygen present in the process stream be at least 50% greater than the concentration of H2S in order to facilitate the regeneration reactions (equations 4 through 6). Should insufficient oxygen be present in the process steam, an oxygen source, such as air, may be added to achieve the desired O2 level. Water is necessary in order to hydrate the metal sulfide complex, allowing for the regeneration reactions (with oxygen) to proceed.
Should it not be feasible to add oxygen, the H2S removal media can be regenerated by taking the media off-line and exposing the spent media to air at the target flow rate and temperature for the duration necessary to regenerate the media.
Metal complexes that are able to facilitate the removal of H2S (e.g., iron) are typically loaded onto the external surface or dispersed within the pores of a substrate to yield a material with a capacity to remove H2S via the above chemical reaction. Examples of porous substrates include activated carbon, silicon dioxide and aluminum oxide. Iron sponge, namely iron oxide or hydroxide loaded onto wood chips or shavings, is also employed in the removal of H2S from process streams. While said materials may be considered effective, they are limited in their capacity to remove H2S by the amount of metal that can be effectively incorporated into the substrate. Therefore, metal loadings are limited to typically on the order of 10% by weight. This often limits the capacity of the material for the removal of H2S to typically on the order of 20% by weight H2S on a mass basis. The capacity is limited because the reactive site becomes hindered due to the presence of product elemental sulfur. Mixed metal oxy-hydroxides have the potential to overcome these deficiencies by having the structure comprised of reactive moieties.